This invention relates generally to video monitors and particularly to video monitors that are capable of operation in a plurality of modes.
The use of video monitors has grown rapidly with the proliferation of computer terminals. Those monitors of greatest interest to this invention are so-called high resolution monitors that are used for the display of data. Monitors generally have a non-standard display format (as compared with television cathode ray tube displays) and often utilize different horizontal and vertical scanning frequencies. The availability of different data output formats from computers and different color graphics boards for use in monitors present a problem to manufacturers. Since the various formats and graphics boards may entail the use of different horizontal frequencies and vertical resolutions, monitor manufacturers who wish to supply equipment that is operable with a wide range of computer terminals must provide suitable accommodation means.
In particular, a monitor system that is capable of displaying information with a single horizontal frequency of 31.5 KHz and any of three different vertical formats (resolutions) has been announced. The three vertical formats are 350 lines, 400 lines and 480 lines. The particular format used is encoded by the polarity of the incoming horizontal and vertical sync signals.
This situation challenges a manufacturer who wants to market a single video monitor that is capable of operation with input data formatted in any of the different modes. Clearly, separate deflection and sync signal processing circuits, i.e., ones that are individually tailored to a particular piece of equipment, impose heavy inventory and cost burdens. The present invention solution utilizes a PROM (programmable read only memory) that has a plurality of input signal-accessible memory locations, at each of which output data is stored, for providing mode signals based upon the polarities of the incoming sync signals and the correct polarity sync signals for use by the monitor apparatus. While in the preferred embodiment, a PROM is utilized, it will be readily apparent that any type memory means ma be substituted.